When propeller driven aircrafts, especially airplanes, take off or turn in flight, their propeller shaft is placed under extremely high loads. Forces from these loads are, desirably, partly absorbed by the propeller shaft and partly transferred to thrust and rotational bearings which support the propeller shaft. However, some of these forces are undesirably transferred to the gear train connecting the propeller shaft to the crankshaft, the crankshaft itself, and other engine parts, e.g., connecting rods, pistons, and crankshaft bearings and seals. If the propeller shaft is poorly balanced, the undesired transferred forces tend to be higher and more concentrated, and additional forces due to the instability of the propeller shaft may also be transferred to these components. Many of these components are not designed to accommodate such forces. Consequently, the effective life of these components is reduced and the servicing and replacement of these components must be done more frequently. Further, the failure of one of these components in flight or during take off may cause the plane to crash, possibly resulting in human injuries and deaths and significant property damage.
A prior art airplane engine and propeller drive arrangement 10 for an airplane 13 is schematically shown in FIG. 1. Arrangement 10 includes a combustion airplane engine 11, a crankshaft 14, a transfer case 20, and a propeller shaft 22 with a propeller 23 mounted at the forward end thereof. Engine 11 includes a crankcase 12, and crankshaft 14 is journalled therein by a plurality of bearings 16.
Transfer case 20 is mounted to the outside of front wall 18 of crankcase 12, either directly or by supports 21. Crankshaft 14 penetrates front wall 18 of crankcase 12 and extends into transfer case 20. Propeller shaft 22 is journalled in transfer case 20 by a plurality of supported bearings 24. Inside transfer case 20, a gear train 25, consisting of gears 26, 27, and 28, rotatably couples crankshaft 14 to propeller shaft 22. Rotational power transferred from crankshaft 14 to propeller shaft 22 with propeller 23 thereon provides propulsive thrust for airplane 13.
During flight, torsional and other forces are encountered by propeller 23 and propeller shaft 22 due to wind resistance and various other loads. These forces can be very significant, especially when the airplane is taking off or turning in flight. In this prior art arrangement 10, propeller shaft 22 is proportionally short and is journalled in transfer case 20 by bearings 24 which can only be spaced over a relatively short distance d.sub.1. This limits the ability of propeller shaft 22 to absorb a large portion of these forces and reduces the ability to support and balance propeller shaft 22 by bearings spaced over a large distance. Consequently, these forces and forces resulting from any instability of propeller shaft 22 are undesirably transferred to gears 26, 27, and 28 in gear train 25, crankshaft 14 via gear train 25, and many other engine parts via crankshaft 14. These components are typically not designed to handle such forces. Therefore, arrangement 10 requires frequent servicing and replacement of parts. In addition, as previously mentioned, the failure of some of these components in flight or during take off could lead to catastrophic results.
Another drawback of this prior art arrangement is the transfer of large vibrational forces to the airplane body, and more specifically the airplane cabin, when the airplane is taking off or turning in flight.
Therefore, it would be advantageous to have an aircraft engine arrangement which enhances the balancing and support of the propeller shaft to reduce the loads on the bearings, gears, seals, crankshaft, and other engine components, thereby increasing the service life of these components.